A profile that enables perceptual rendering and transcends the actual device needs to represent the desired appearance. It is difficult to know how to generate such a profile. It is helpful to conceptualize a "reference medium" which is a hypothetical medium on which the colors are being rendered. It has a large gamut and dynamic range which approximate the limits of current reflection-print technology. It is described using "realworld" specifications so that even though the medium is not real, it can be treated as if it were real. It is also necessary to define a "reference viewing environment" which is the environment in which the reference medium is to be viewed. This environment is used to determine the observer's adaptation state and establishes the connection between color stimulus and color appearance.